Microfluidic devices and systems of such devices employ small capillaries or microchannels attached or integrated with a solid substrate to perform a variety of operations in a number of analytical chemical and biochemical applications on a very small scale. For example, integrated microfluidic devices can first employ electrical fields to effectively separate nucleic acids, proteins or other macromolecules of interest and then use microscale detection systems for characterization and analysis of the separation products. Such microfluidic devices accomplish these operations using remarkably small reaction volumes that can be at least several orders of magnitude smaller than conventional methods. The small size of these systems allows for increased reaction rates that use less reagent volume and that take up far less laboratory or industrial space. Microfluidic systems thus offer the potential for attractive efficiency gains, and consequently, substantial economic advantages.
Microfluidic devices are particularly well-suited to conduct analytical methods that employ spectroscopic detection systems. A variety of spectroscopic techniques can be employed in conjunction with microfluidic devices, including infrared (IR), visible light, ultraviolet (UV), X-ray, microwave, electron beam, ion beam, positron emission, nuclear magnetic resonance (NMR), as well as various adsorption, emission, fluorescence, surface plasmon resonance (SPR), polarization, and light scattering spectroscopy, such as Raman spectroscopy. The particular technique employed will depend on the particular application. In research or industrial settings, microfluidic devices are typically employed in biochemical or cell-based assays that use spectroscopic detection systems to quantify labeled or unlabeled molecules of interest. For example, such an assay measures the expression of green fluorescent protein in mammalian cells following treatment by a candidate small molecule or biologic drug of interest. Another example is the use of the quantitative polymer chain reaction technique (PCR) in microfluidics devices for gene amplification and analysis with intercalating fluorescence dye as the spectroscopic indicator. Other examples include, but are not limited to, enzymatic and biochemical reactions in general, chemical reactions, phase transition detections, etc.
Microfluidic devices generally employ networks of integrated microscale channels and reservoirs in which materials are transported, mixed, separated and detected, with various detectors and sensors embedded or externally arranged for quantification, as well as actuators and other accessories for manipulations of the fluidic samples. The development of sophisticated material transport systems has permitted the development of systems that are readily automatable and highly reproducible. Such operations are potentially automatable and can be incorporated into high-throughput systems with tremendous advantages for numerous industrial and research applications. Microfluidic devices often use plastics as the substrate. While polymeric materials offer advantages of easy fabrication, low cost and availability, they tend to be fluorescent. For example, when irradiating a sample with excitation light, light scatter may result in a significant background signal, particularly when the excitation pathway and emission pathway are the same. Other materials, such as glass, silicon, and metal may be used as well.